High solids acid etch resistant clear coating composition

ABSTRACT

The present invention provides for an etch and mar resistant low VOC clear coating composition most suitable for use as a top clear coat in multi-layered OEM or refinish automative coatings. The coating composition includes isocyanate, silane and melamine components. The isocyanate component includes an aliphatic polyisocyanate. The composition may be formulated as a two-pack or one-pack coating composition, wherein the isocyanante functionalities are blocked with a blocker such as a mono-alcohol.

CROSS-REFERENCE TO PARENT APPLICATIONS

This application is a 35 U.S.C. §371 of PCT/US00/06963 filed on Mar. 16,2000, which claims benefit of provisional Application Serial Nos.60/124,850, filed Mar. 17, 1999 and No. 60/175,728, filed Jan. 1, 2000.

BACKGROUND OF THE INVENTION

The present invention generally relates to high solids, low VOC(volatile organic component) coating compositions and more particularlyto low VOC clear coating compositions suited for multi-layered coatingsused in automotive OEM and refinish applications.

Basecoat-clearcoat systems have found wide acceptance in the automotivefinishes market. Continuing effort has been directed to improve theoverall appearance, the clarity of the topcoat, and the resistance todeterioration of these coating systems at ever-higher application solidslevels. Further effort has also been directed to the development ofcoating compositions having low VOC. A continuing need still exists forclear coating formulations having an outstanding balance of performancecharacteristics after application, particularly gloss and distinctnessof image (DOT) at high solids levels. Melamine/acrylic polyolcrosslinked or melamine self-condensed coatings for example, may providecoatings having acceptable mar but such coatings have poor acid etchresistance and decreased appearance at higher solids levels. On theother hand, isocyanate/acrylic polyol based 2K urethane coatingsgenerally provide acceptable acid-etch resistance but such coatings havepoor mar resistance. Therefore, a need still exists for coatings thatnot only provide acceptable mar and acid-etch resistance but also highgloss and DOI at the lowest VOC possible.

One approach described by Ntsihlele and Pizzi in an article titled“Cross-Linked Coatings by Co-Reaction of Isocyanate-MethoxymethylMelamine System” (Journal of Applied Polymer Science, Volume 55, Pages153-161-1995) provides for reacting aromatic diisocyanate withmethoxymethyl melamine. However, a need still exists for a high solidsclear coating composition, which upon a long-term exposure to sunlightdoes not yellow or become brittle and provides high gloss and DOI.

Another approach described in a commonly assigned WO-A-96/25466 isdirected to a coating composition that includes a component having atleast two acid groups, a polymer having both epoxy and silanefunctionality and an acrylic core polymer having stabilizer componentssoluble in solvent used in the coating composition.

Yet another approach described in U.S. Pat. No. 4,315,091 is directed tocoating compositions suitable for coating delicate substrate, such aspolycarbonate, that can be readily attacked by organic solvents. Thecomposition contains a partially hydroxyzed siloxane compound.

STATEMENT OF THE INVENTION

The present invention is directed to a clear coating compositioncomprising isocyanate, silane and melamine components wherein saidisocyanate component comprises an aliphatic polyisocyanate having on anaverage 2 to 6 isocyanate functionalities.

The present invention is also directed to a method of producing a clearcoating on a substrate comprising:

applying a layer of a clear coating composition comprising isocyanate,silane and melamine components wherein said isocyanate componentcomprises an aliphatic polyisocyanate having on an average 2 to 6isocyanate functionalities; and

curing said layer into said clear coating.

One of the advantages of the present invention is its low VOC, which isbelow the current guidelines of Environment Protection Agency (EPA) ofthe United States.

Another advantage is the mar and etch resistance and hardness of thecoating resulting from the coating composition of the present invention.

Yet another advantage is the clarity and high gloss of the coatingresulting from the coating composition of the present invention. As usedherein:

“Two-pack coating composition” means a thermoset coating compositioncomprising two components stored in separate containers. Thesecontainers are typically sealed to increase the shelf life of thecomponents of the coating composition. The components are mixed prior touse to form a pot mix. The pot mix has a limited pot life typically afew minutes (15 minutes to 45 minutes) to a few hours (4 hours to 6hours). The pot mix is applied as a layer of desired thickness on asubstrate surface, such as an autobody. After application, the layer iscured under ambient conditions or bake cured at elevated temperatures toform a coating on the substrate surface having desired coatingproperties, such as high gloss, mar-resistance and resistance toenvironmental etching.

“One-pack coating composition” means a thermoset coating compositioncomprising two components that are stored in the same container.However, one component is blocked to prevent premature crosslinking.After the application of the one-pack coating composition on asubstrate, the layer is typically exposed to elevated temperatures tounmask the blocked component. Thereafter, the layer is bake-cured atelevated temperatures to form a coating on the substrate surface havingdesired coating properties, such as high gloss, mar-resistance andresistance to environmental etching.

“Low VOC coating composition” means a coating composition that includesin the range of from 0 to 0.472 kilogram of organic solvent per liter (4pounds per gallon), preferably in the range of from 0.118 (1 pound pergallon) to 0.178 kilogram of organic solvent per liter (1.5 pounds pergallon) of the composition, as determined under the procedure providedin ASTM D3960.

“High solids composition” means a coating composition having a solidcomponent in the range of from 65 to 100 percent and preferably greaterthan 70 percent, all in weight percentages based on the total weight ofthe composition.

“Clear coating composition” means a clear coating composition thatproduces upon cure, a clear coating having DOI (distinctness of image)rating of more than 80 and 20° gloss rating of more than 80.

“GPC weight average molecular weight” and “GPC number average molecularweight” means a weight average molecular weight and a weight averagemolecular weight, respectively measured by utilizing gel permeationchromatography. A high performance liquid chromatograph (HPLC) suppliedby Hewlett-Packard; Palo Alto, Calif. was used. Unless stated otherwise,the liquid phase used was tetrahydrofuran and the standard waspolymethyl methacrylate.

“Polymer particle size” means the diameter of the polymer particlesmeasured by using a Brookhaven Model BI-90 Particle Sizer supplied byBrookhaven Instruments Corporation, Holtsville, N.Y. The sizer employs aquasi-elastic light scattering technique to measure the size of thepolymer particles. The intensity of the scattering is a function ofparticle size. The diameter based on an intensity weighted average isused. This technique is described in Chapter 3, pages 48-61, entitledUses and Abuses of Photon Correlation Spectroscopy in Particle Sizing byWeiner et al. 1987 edition of American Chemical Society Symposiumseries.

“Polymer solids” or “composition solids” means a polymer or compositionin its dry state.

“Aliphatic” as employed herein includes aliphatic and cycloaliphaticmaterials.

“Crosslinkable” means that the individual components of an adductcontain functionalities which react within the composition of theinvention to give a coating of good appearance, durability, hardness andmar resistance.

“Acid etch resistance” refers to the resistance provided by a coatedsurface against chemical etching action by the environment, such as forexample acid rain.

“Mar resistance” refers to the resistance provided by coating tomechanical abrasions, such as, for example, the abrasion of a coatedsurface, such as an automotive body, that typically occurs duringwashing and cleaning of the coated surface.

Applicants have unexpectedly discovered that contrary to conventionalapproaches used in typical thermoset coating compositions, i.e., thoseinvolving polymers and crosslinking components, a very viable route liesin a combination of what would traditionally be considered ascrosslinking agents for producing a unique low VOC high solids clearcoating composition that produces coatings having superior coatingproperties, such as clarity, and mar and etch resistance. Applicantshave further unexpectedly discovered that by including a silanecomponent in a clear coating composition, the solids level can befurther increased without sacrificing the etch and mar resistance,gloss, DOI, and other desired coating properties. It is believed thatthe silane component acts as a substitute for a solvent typically usedin a coating composition and reacts upon cure to generate a stable anddurable crosslinking structure. Thus, the viscosity of the resultingcoating composition can be substantially lowered without sacrificingcoating properties.

The clear coating composition includes isocyanate, silane and melaminecomponents. The isocyanate component includes an aliphaticpolyisocyanate having on an average 2 to 6, preferably 2.5 to 6 and morepreferably 3 to 4 isocyanate functionalities. The coating compositionincludes in the range of from 35 percent to 70 percent, preferably inthe range of from 40 percent to 60 percent, and most preferably in therange of 45 percent to 55 percent of the aliphatic polyisocyanate, thepercentages being in weight percentages based on the total weight ofcomposition solids.

Examples of suitable aliphatic polyisocyanates include aliphatic orcycloaliphatic di-, tri- or tetra-isocyanates, which may or may not beethylenically unsaturated, such as 1,2-propylene diisocyanate,trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylenediisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate,2,2,4-trimethyl hexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, omega-dipropyl ether diisocyanate, 1,3-cyclopentane diisocyanate,1,2-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophoronediisocyanate, 4-methyl-1,3-diisocyanatocyclohexane, trans-vinylidenediisocyanate, dicyclohexylmethane-4,4′-diisocyanate,3,3′-dimethyl-dicyclohexylmethane 4,4′-diisocyanate,meta-tetramethylxylylene diisocyanate, polyisocyanates havingisocyanurate structural units such as the isocyanurate of hexamethylenediisocyanate and isocyanurate of isophorone diisocyanate, the adduct of2 molecules of a diisocyanate, such as hexamethylene diisocyanate,uretidiones of hexamethylene diisocyanate, uretidiones of isophoronediisocyanate or isophorone diisocyanate, and a diol such as ethyleneglycol, the adduct of 3 molecules of hexamethylene diisocyanate and 1molecule of water (available under the trademark Desmodur® N of BayerCorporation, Pittsburgh, Pa.).

Aromatic polyisocyanates are not suitable for use in the presentinvention as the clear coatings resulting therefrom are too lightsensitive and tend to yellow with age and crack upon long term exposureto sunlight. As a result such clear coatings are not durable.

If desired, the isocyanate functionalities of the polymeric isocyanatemay be capped with a monomeric alcohol to prevent premature crosslinkingin a one-pack composition. Some suitable monomeric alcohols includemethanol, ethanol, propanol, butanol, isopropanol, isobutanol, hexanol,2-ethylhexanol and cyclohexanol.

The melamine component of the coating composition includes suitablemonomeric or polymeric melamines or a combination thereof. Alkoxymonomeric melamines are preferred. The coating composition includes inthe range of from 10 percent to 40 percent, preferably in the range offrom 15 percent to 35 percent, and most preferably in the range of fromof 20 percent to 30 percent of the melamine, the percentages being inweight percentages based on the total weight of composition solids.

In the context of the present invention, the term “alkoxy monomericmelamine” means a low molecular weight melamine which contains, on anaverage three or more methylol groups etherized with a C_(1 to 5)monohydric alcohol such as methanol, n-butanol, or isobutanol pertriazine nucleus, and has an average degree of condensation up to about2 and preferably in the range of about 1.1 to about 1.8, and has aproportion of mononuclear species not less than about 50 percent byweight. The polymeric melamines have an average degree of condensationof more than 1.9

Some of such suitable monomeric melamines include highly alkylatedmelamines, such as methylated, butylated, isobutylated melamines andmixtures thereof. More particularly hexamethylol melamine, trimethylolmelamine, partially methylated hexamethylol melamine, andpentamethoxymethyl melamine are preferred. Hexamethylol melamine andpartially methylated hexamethylol melamine are more preferred andhexamethylol melamine is most preferred.

Many of these suitable monomeric melamines are supplied commercially.For example, Cytec Industries Inc., West Patterson, N.J. supplies Cymel®301 (degree of polymerization of 1.5, 95% methyl and 5% methylol),Cymel® 350 (degree of polymerization of 1.6, 84% methyl and 16%methylol), 303, 325, 327 and 370, which are all monomeric melamines.Suitable polymeric melamines include high amino (partially alkylated,—N, —H) melamine known as Resimene™ BMP5503 (molecular weight 690,polydispersity of 1.98, 56% buytl, 44% amino), which is supplied bySolutia Inc., St. Louis, Mo., or Cymel® 1158 provided by CytecIndustries Inc., West Patterson, N.J.

Cytec Industries Inc. also supplies Cymel® 1130 @ 80 percent solids(degree of polymerization of 2.5), Cymel® 1133 (48% methyl, 4% methyloland 48% butyl), both of which are polymeric melamines.

The coating composition preferably includes one or more catalysts toenhance crosslinking of the components on curing. Generally, the coatingcomposition includes in the range of from 0.1 percent to 5 percent,preferably in the range of from 0.1 to 2 percent, more preferably in therange of from 0.5 percent to 2 percent and most preferably in the rangeof from 0.5 percent to 1.2 percent of the catalyst, the percentagesbeing in weight percentages based on the total weight of compositionsolids.

Some of the suitable catalysts include the conventional acid catalysts,such as aromatic sulfonic acids, for example dodecylbenzene sulfonicacid, para-toluenesulfonic acid and dinonylnaphthalene sulfonic acid,all of which are either unblocked or blocked with an amine, such asdimethyl oxazolidine and 2-amino-2-methyl-1-propanol,n,n-dimethylethanolamine or a combination thereof. Other acid catalyststhat can be used are strong acids, such as phosphoric acids, moreparticularly phenyl acid phosphate, which may be unblocked or blockedwith an amine.

In addition to the foregoing, the coating composition preferablyincludes a small amount of one or more organo tin catalysts, such asdibutyl tin dilaurate, dibutyl tin diacetate, stannous octate, anddibutyl tin oxide. Dibutyl tin dilaurate is preferred. The amount oforgano tin catalyst added generally ranges from 0.001 percent to 0.5percent, preferably from 0.05 percent to 0.2 percent and more preferablyfrom 0.1 percent to 0.15 percent, the percentages being in weightpercentages based on the total weight of composition solids.

These catalysts are preferably added to the melamine component.

The silane component of the coating composition generally includes apolymer provided with at least one reactive silane group. The coatingcomposition includes in the range of from 5 percent to 45 percent,preferably in the range of from 10 percent to 40 percent, and mostpreferably in the range of from of 15 percent to 35 percent of thesilane component, the percentages being in weight percentages based onthe total weight of composition solids.

The silane polymers suitable for use in the present invention haveweight average molecular weight in the range of about 100 to 30,000,preferably in the range of about 120 to 25,000 and more preferably inthe range of about 150 to 7,500. All molecular weights disclosed hereinare determined by gel permeation chromatography using a polystyrenestandard.

The silane polymer suitable herein is a polymerization product of about30 to 95%, preferably 40 to 60%, by weight of ethylenically unsaturatednon-silane containing monomers and about 5 to 70%, preferably 40 to 60%,by weight of ethylenically unsaturated silane containing monomers, basedon the weight of the silane polymer. Suitable ethylenically unsaturatednon-silane containing monomers are alkyl acrylates, alkyl methacrylatesand any mixtures thereof, where the alkyl groups have 1 to 12 carbonatoms, preferably 3 to 8 carbon atoms.

Suitable alkyl methacrylate monomers used to form the silane polymerinclude methyl methacrylate, ethyl methacrylate, propyl methacrylate,butyl methacrylate, isobutyl methylate, pentyl methacrylate, hexylmethacrylate, octyl methacrylate, nonyl methacrylate, and laurylmethacrylate. Similarly, suitable alkyl acrylate momomers include methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutylacrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, nonylacrylate, and lauryl acrylate. Cycloaliphatic methacrylates andacrylates also can be used, for example, such as trimethylcyclohexylmethacrylate, trimethylcyclohexyl acrylate, iso-butyl methacrylate,t-butyl cyclohexyl acrylate, or t-butyl cyclohexyl methacrylate. Arylacrylate and aryl methacrylates, such as, for example benzyl acrylateand benzyl methacrylate can be also used. It is understood thatcombinations of the foregoing monomers are also suitable.

In addition to alkyl acrylates or methacrylates, other polymerizablenon-silane-containing monomers, up to about 50% by weight of thepolymer, can be used in the silane polymer for the purpose of achievingthe desired properties such as hardness, appearance, and mar resistance.Exemplary of such other monomers are styrene, methyl styrene,acrylamide, acrylonitrile and metharcylonitrile. Styrene may be used inthe range of 0 to 50%, preferably 5% to 30% by weight of the silanepolymer.

A suitable silane containing monomer useful in forming the silanepolymer is an alkoxysilane having the following structural formula:

wherein R is either CH₃, CH₃CH₂, CH₃O, or CH₃CH₂O; R₁ and R₂ are CH₃ orCH₃CH₂; and R₃ is either H, CH₃, or CH₃CH₂; and n is 0 or a positiveinteger. from 1 to 10, preferably from 1 to 4. Preferably, R is CH₃O orCH₃CH₂O and n is 1.

Typical examples of such alkoxysilanes are the acrylatoalkoxy silanes,such as gamma-acryloxypropyltrimethoxy silane and the methacrylatoalkoxysilanes, such as gamma-methacryloxypropyltrimethoxy silane, andgamma-methacryloxypropyltris(2-methoxyethoxy)silane.

Other suitable alkoxy silane monomers have the following structuralformula:

wherein R, R₁ and R₂ are as described above and n is a positive integerfrom 1 to 10, preferably from 1 to 4. Examples of such alkoxysilanes arethe vinylalkoxy silanes, such as vinyltrimethoxy silane, vinyltriethoxysilane and vinyltris(2-methoxyethoxy)silane.

Other suitable silane containing monomers are acyloxysilanes, includingacrylatoxy silane, methacrylatoxy silane and vinylacetoxy silanes, suchas vinylmethyldiacetoxy silane, acrylatopropyltriacetoxy silane, andmethacrylatopropyltriacetoxy silane. It is understood that combinationsof the above-mentioned silane containing monomers are also suitable.

Consistent with the aforedescribed components of the silane polymer, oneparticular example of a silane polymer useful in the coating compositionof this invention may contain the following constituents: about 15 to25% by weight styrene, about 30 to 60% by weightmethacryloxypropyltrimethoxy silane, and about 25 to 50% by weighttrimethylcyclohexyl methacrylate.

One preferred silane polymer contains about 30% by weight styrene, about50% by weight methacryloxypropyl trimethoxy silane, and about 20% byweight of nonfunctional acrylates or methacrylates such astrimethylcyclohexyl methacrylate, butyl acrylate, and iso-butylmethacrylate and any mixtures thereof.

Silane functional macromonomers also can be used in forming the silanepolymer. These macromonomers are the reaction product of a silanecontaining compound, having a reactive group such as epoxide orisocyanate, with an ethylenically unsaturated non-silane containingmonomer having a reactive group, typically a hydroxyl or an epoxidegroup, that is co-reactive with the silane monomer. An example of auseful macromonomer is the reaction product of a hydroxy functionalethylenically unsaturated monomer such as a hydroxyalkyl acrylate ormethacrylate having 1 to 4, preferably 2 to 3 carbon atoms in the alkylgroup and an isocyanatoalkyl alkoxysilane such as isocyanatopropyltriethoxysilane.

Typical of such above-mentioned silane functional macromonomers arethose having the following structural formula:

wherein R, R₁, and R₂ are as described above; R₄ is 1 or CH₃, R₃ is analkylene group having 1 to 8, preferably 1 to 4 carbon atoms and n is apositive integer from 1 to 8, preferably from 1 to 4.

The coating composition of the present invention, which is formulatedinto high solids coating systems further contains at least one organicsolvent typically selected from the group consisting of aromatichydrocarbons such as petroleum naphtha or xylenes; ketones such asmethyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone oracetone; esters such as butyl acetate or hexyl acetate; and glycol etheresters, such as propylene glycol monomethyl ether acetate. The amount oforganic solvent added depends upon the desired solids level as well asthe desired amount of VOC of the composition. If desired, the organicsolvent may be added to both components of the binder.

The coating composition of the present invention may also containconventional additives such as stabilizers and rheology control agents,flow agents, and toughening agents. Such additional additives will, ofcourse, depend on the intended use of the coating composition. Anyadditives that would adversely effect the clarity of the cured coatingwill not be included as the composition is used as a clear coating. Theforegoing additives may be added to either component or both, dependingupon the intended use of the coating composition.

The clear coating composition of the present invention may be suppliedin the form of a two-pack coating composition in which the first-packincludes the polyisocyanate component and the second-pack includes themelamine component. Generally the first and the second pack are storedin separate containers and mixed before use. The containers arepreferably sealed air tight to prevent degradation during storage. Themixing may be done, for example, in a mixing nozzle or in a container.

Alternatively, when the isocyanate functionalities of the polyisocyanateare blocked, both the components of the coating composition can bestored in the same container in the form of a one-pack coatingcomposition.

To improve weatherability of the clear finish of the coatingcomposition, about 0.1 to 5%, by weight, based on the weight of thecomposition solids, of an ultraviolet light stabilizer or a combinationof ultraviolet light stabilizers and absorbers may be added. Thesestabilizers include ultraviolet light absorbers, screeners, quenchersand specific hindered amine light stabilizers. Also, about 0.1 to 5% byweight, based on the weight of the composition solids, of an antioxidantcan be added. Typical ultraviolet light stabilizers that are usefulinclude benzophenones, such as hydroxydodecyclbenzo-phenone,2,4-dihydroxybenzophenone; triazoles, such as2-phenyl-4-(2′-4′-dihydroxybenzoyl)triazoles; and triazines, such as3,5-dialkyl-4-hydroxyphenyl derivatives of triazine and triazoles suchas 2-(benzotriazole-2-yl)-4,6-bis(methylethyl-1-phenyl ethyl)phenol,2-(3-hydroxy-3,5′-di-tert amyl phenyl)benzotriazole,2-(3′,5′-bis(1,1-dimethylpropyl)-2′-hydroxyphenyl)-2H-benzotriazole,benzenepropanoic acid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C₇₋₉-branchedalkyl esters, and2-(3′,5′-bis(1-methyl-1-phenylethyl)-2′-hydroxyphenyl)benzotriazole.

Typical hindered amine light stabilizers arebis(2,2,6,6-tetramethylpiperidinyl)sebacate,bis(N-methyl-2,2,6,6-tetramethylpiperidinyl)sebacate andbis(N-octyloxy-2,2,6,6-tetramethylpiperidynyl)sebacate. One of theuseful blends of ultraviolet light absorbers and hindered amine lightstabilizers is bis(N-octyloxy-2,2,6,6-tetramethylpiperidynyl)sebacateand benzenepropanoic acid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-,C7-9-branchedalkyl esters. Another useful blend of ultraviolet light absorbers andhindered amine light stabilizers is2-(3′,5′-bis(1-methyl-1-phenylethyl)-2′-hydroxyphenyl)benzotriazole anddecanedioc acid,bis(2,2,6,6,-tetramethyl-4-piperidinyl)ester bothsupplied by Ciba Specialty Chemicals, Tarrytown, N.Y. under thetrademark Tinuvin® 900 and Tinuvin® 123, respectively.

The coating composition of the present invention optionally contains inthe range of from 0.1 percent to 40 percent, preferably in the range offrom 5 percent to 35 percent, and more preferably in the range of from10 percent to 30 percent of a flow modifying resin, such as anon-aqueous dispersion (NAD), all percentages being based on the totalweight of composition solids. The weight average molecular weight of theflow modifying resin generally varies in the range of from 20,000 to100,000, preferably in the range of from 25,000 to 80,000 and morepreferably in the range from 30,000 to 50,000.

The non-aqueous dispersion-type resin is prepared bydispersion-polymerizing at least one vinyl monomer in the presence of apolymer dispersion stabilizer and an organic solvent. The polymerdispersion stabilizer may be any of the known stabilizers used commonlyin the field of non-aqueous dispersions, and may include the followingsubstances (1) through (9) as examples:

(1) A polyester macromer having about 1.0 polymerizable double bondwithin the molecule as obtainable upon addition of glycidyl acrylate orglycidyl methacrylate to an auto-condensation polyester of ahydroxy-containing fatty acid such as 12-hydroxystearic acid.

(2) A comb-type polymer prepared by copolymerizing the polyestermacromer mentioned under (1) with methyl methacrylate and/or other(meth)acrylic ester or a vinyl monomer.

(3) A polymer obtainable by the steps of copolymerizing the polymerdescribed under (2) with a small amount of glycidyl(meth)acrylate and,then, adding (meth)acrylic acid to the glycidyl groups thereof so as tointroduce double bonds.

(4) A hydroxy-containing acrylic copolymer prepared by copolymerizing atleast 20 percent by weight of (meth)acrylic ester of a monohydricalcohol containing 4 or more carbon atoms.

(5) An acrylic copolymer obtainable by producing at least 0.3 doublebond per molecule based on its number average molecular weight, into thecopolymer mentioned under (4). A method for introducing double bondsmay, for example, comprise copolymerizing the acrylic polymer with asmall amount of glycidyl(meth)acrylate and then adding (meth)acrylicacid to the glycidyl group.

(6) An alkylmelamine resin with a high tolerance to mineral spirit.

(7) An alkyd resin with an oil length not less than 15 percent and/or aresin obtainable by introducing polymerizable double bonds into thealkyd resin. A method of introducing double bonds may, for example,comprise addition reaction of glycidyl(meth)acrylate to the carboxylgroups in the alkyd resin.

(8) An oil-free polyester resin with a high tolerance to mineral spirit,an alkyd resin with an oil length less than 15 percent, and/or a resinobtainable by introducing double bonds into said alkyd resin.

(9) A cellulose acetate butyrate into which polymerizable double bondshave been introduced. An exemplary method of introducing double bondscomprises addition reaction of isocyanatoethyl methacrylate to celluloseacetate butyrate.

These dispersion stabilizers can be used alone or in combination.

Among the aforementioned dispersion stabilizers, preferred for thepurposes of the invention are those which can be dissolved incomparatively low polar solvents, such as aliphatic hydrocarbons toassure the film performance requirements to some extent. As dispersionstabilizers which can meet such conditions, the acrylic copolymersmentioned under (4) and (5) are desirable in that they not only lendthemselves well to adjustment of molecular weight, glass transitiontemperature, polarity (polymer SP value), hydroxyl value, acid value andother parameters but are excellent in weatherability. More desirable areacrylic copolymers containing an average of about 0.2 to about 1.2polymerizable double bonds, per molecule, which are graft copolymerizedwith dispersed particles.

The non-aqueous dispersion-type resin used in accordance with thisinvention can be easily prepared by dispersion-polymerizing at least onevinyl monomer in the presence of the aforedescribed polymer dispersionstabilizer and an organic solvent, which mainly contains an aliphatichydrocarbon. The dispersion stabilizer and the vinyl monomer are solublein the organic solvent. However, the polymer particles formed by thevinyl monomer are not soluble in the solvent.

The monomer component forming the acrylic copolymer suitable as thepolymer dispersion stabilizer and the vinyl monomer forming thedispersed L particles may be virtually any radical-polymerizableunsaturated monomer. A variety of monomers can be utilized for thepurpose. Typical examples of such monomers include the following.

(a) Esters of acrylic acid or methacrylic acid, such as for example,C₁₋₁₈ alkyl esters of acrylic or methacrylic acid, such as methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butylacrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, stearylacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, octylmethacrylate, lauryl methacrylate, and stearyl methacrylate; glycidylacrylate and glycidyl methacrylate; C₂₋₈ alkenyl esters of acrylic ormethacrylic acid, such as alkyl acrylate, and alkyl methacrylate; C₂₋₈hydroxyalkyl esters of acrylic or methacrylic acid, such as hydroxyethylacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, andhydroxypropyl methacrylate; and C₃₋₁₈ alkenyloxyalkyl esters or acrylicor methacrylic acid, such as alkyloxyethyl acrylate, and alkyloxyethylmethacrylate.

(b) Vinyl aromatic compounds, such as, for example, styrene,α-methylstyrene, vinyltoluene, p-chlorostyrene, and vinylpyridine.

(c) α,β-Ethylenically unsaturated acids, such as, for example, acrylicacid, methacrylic acid, itaconic acid and crotonic acid.

(d) Amides of acrylic or methacrylic acid, such as, for example,acrylamide, methacrylamide, n-butoxymethylacrylamide,N-methylolacrylamide, n-butoxymethylmethacrylamide, andN-methylolmethacrylamide.

(e) Others: for example, acrylonitrile, methacrylonitrile, methylisopropenyl ketone, vinyl acetate, VeoVa monomer (product of ShellChemicals, Co., Ltd.; mixed vinyl esters of a synthetic saturatedmonocarboxylic acid of highly branched structure containing ten carbonatoms), vinyl propionate, vinyl pivalate, isocyanatoethyl methacrylate,perfluorocyclohexyl(meth)acrylate, p-styrenesulfonamide,N-methyl-p-styrenesulfonamide, and γ-methacryloyloxypropyl trimethoxysilane.

Among the monomers mentioned above, the following materials can be usedwith particular advantage for the preparation of the acrylic copolymerused as a dispersion stabilizer:

Mixed monomers based on comparatively long-chain, low-polar monomers,such as n-butyl methacrylate, 2-ethylhexyl methacrylate, dodecylmethacrylate, lauryl methacrylate, and stearyl methacrylate,supplemented as necessary with styrene, methyl(meth)acrylate,ethyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, propyl(meth)acrylate,and (meth)acrylic acid. The dispersion stabilizer may be one prepared byadding glycidyl(meth)acrylate or isocyanatoethyl methacrylate to acopolymer of the monomers for introduction of polymerizable doublebonds.

The acrylic copolymer used as the dispersion stabilizer can be easilyprepared using a radical polymerization initiator in accordance with theknown solution polymerization process.

The number average molecular weight of the dispersion stabilizer ispreferably in the range of about 1,000 to about 50,000 and, for stillbetter results, about 3,000 to about 20,000.

Among the monomers mentioned above, particularly preferred vinylmonomers for the formation of the dispersed polymer particlespredominantly contain comparatively high-polarity monomers, such asmethyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, andacrylonitrile, supplemented as necessary with (meth)-acrylic acid, and2-hydroxyethyl(meth)acrylate. It is also possible to provide gelparticles as cross-linked in molecules by copolymerizing a small amountof polyfunctional monomers, such as divinylbenzene, and ethylene glycoldimethacrylate, by copolymerizing a plurality of monomers havingmutually reactive functional groups, such as glycidyl methacrylate andmethacrylic acid, or by copolymerizing an auto-reactive monomer, such asN-alkoxymethylated acrylamides, and γ-methacryloyloxypropyl trimethoxysilanes.

In conducting the dispersion polymerization, the ratio of the dispersionstabilizer to the vinyl monomer forming dispersed particles is selectedfrom the range of about 5/95 to about 80/20 by weight, preferably about10/90 to about 60/40 by weight, and the dispersion polymerization can beconducted in the presence of a radical polymerization initiator by aknown procedure.

While the particle size of the resulting non-aqueous dispersion typeacrylic resin is generally in the range of about 0.05 μm to about 2 μm,the range of about 0.1 μm to about 0.7 μm is preferable from thestability of shelf life and the gloss, smoothness and weatherability ofthe film.

In use, the first-pack of the two-pack coating composition containingthe polyisocyanate and the second-pack containing the melamine andsilane component are mixed just prior to use or about 5 to 30 minutesbefore use to form a pot mix, which has limited pot life of about 10minutes to about 6 hours. Thereafter, it becomes too viscous to permitapplication through conventional application systems, such as spraying.A layer of the pot mix is typically applied to a substrate byconventional techniques, such as spraying, electrostatic spraying,roller coating, dipping or brushing. Generally, a clear coat layerhaving a thickness in the range of from 25 micrometers to 75 micrometersis applied over a metal substrate, such as automotive body, which isoften pre-coated with other coating layers, such as an electrocoat,primer and a basecoat. The two pack coating composition may be bakedupon application for about 60 to 10 minutes at about 80° C. to 160° C.

When the one-pack coating composition containing the blockedpolyisocyanate is used, a layer thereof applied over a substrate usingaforedescribed application techniques, is cured at a baking temperaturein the range of from 80° C. to 200° C., preferably in the range of 80°C. to 160° C., for about 60 to 10 minutes. It is understood that actualbaking temperature would vary depending upon the catalyst and the amountthereof, thickness of the layer being cured and the blocked isocyanatefunctionalities and the melamine utilized in the coating composition.The use of the foregoing baking step is particularly useful under OEM(Original Equipment Manufacture) conditions.

The clear coating composition of the present invention is suitable forproviding clear coatings on variety of substrates, such as metal, woodand concrete substrates. The present composition is especially suitablefor providing clear coatings in automotive OEM or refinish applications.These compositions are also suitable as clear coatings in industrial andmaintenance coating applications.

The invention is illustrated in the following Examples:

EXAMPLES

Blocked Isocyanurate 1

A mixture of 500 parts of methyl amyl ketone, 1211 parts of 2 ethylhexanol and 0.3 part of dibutyl tin dilaurate was heated to 60° C. undernitrogen blanket in a flask fitted with a mixer and a condenser. Then1796 parts of isocyanurate of hexane diisocyanate (Desmodur® 3300 byBayer Corporation) were added to the reaction mixture, which resulted inan exothermic reaction. The exothermal reaction was controlled bymaintaining the reaction temperature at or below 100° C. Then 45 partsof methyl amyl ketone were added. The reaction mixture was held at 90°C. for 1 hour to yield 2 ethyl hexanol blocked isocyanurate of hexanediisocyanate.

Blocked Isocyanurate 2

A mixture of 1044 parts of methyl amyl ketone, 1746 parts ofisocyanurate of hexane diisocyanate (Desmodur®3300 supplied by BayerCorporation, Pittsburgh, Pa.), and 0.3 part of dibutyl tin dilaurate washeated to 80° C. under nitrogen blanket in a flask fitted with a mixerand a condenser. Then 902 parts of cyclohexanol were added to thereaction mixture over a period of 20 minutes, followed by the additionof 45 parts of methyl amyl ketone. The reaction mixture was held at 100°C. for 1.5 hour to yield cyclohexanol blocked isocyanurate of hexanediisocyanate.

Silane Polymer 1

In a flask fitted with a mixer and a condenser, 158 parts of aliphaticsolvent were heated to reflux. A mixture of 140 parts of styrene, 140parts of isobornyl methacrylate, 304 parts ofmethacryloxypropylrimethoxysilane (UCARSIL® A-174 by Witco), 82 parts ofaliphatic solvent and 16 parts of tertiary butyl peracetate were addedover a period of 240 minutes. The reaction mixture was held for 1 hourto yield a polymer containing methacryloxypropylrimethoxysilane.

Silane Polymer 2 (Silane Functional Polyurethane Polymer)

To a 5 liter reactor fitted with heating mantle, stirrer, and undernitrogen blanket, 1035.7 parts of Aromatic 100 solvent, 206.48 parts ofpropylene carbonate (supplied by Huntsman Corporation, Austin, Tex.),and 340.2 parts aminopropyl trimethoxy silane (supplied by OSICorporation, Tarrytown, N.Y.) were charged. The reaction mixture washeated under agitation to 120° C., held 4 hours and then cooled to 100°C. A shot of 570.49 parts of cyclohexanol (supplied by Aldrich ChemicalCompany, Milwaukee, Wis.), 40 parts of Aromatic 100 solvent, and 0.3parts of dibutyltin dilaurate catalyst (supplied by Air Products,Allentown, Pa.) was added. Thereafter, a polyisocyanate solution of1472.7 parts of Desmodur® 3300 polyisocyanate (supplied by BayerCorporation, Pittsburgh, Pa.) with 240 parts Aromatic 100 solvent. Therate of addition was adjusted to control the resulting exothermicreaction by maintaining the reaction temperature at 120° C. The reactionmixture was held at 120° C. for 3.8 hours at which point the isocyanatehad been completely consumed as determined by the absence of theisocyanate absorbance at 2220 cm⁻¹ in the infrared spectrum. Theresulting silane polymer had viscosity of 12,300 cps at 70.52% nv. Itshould be noted that absent the silane functionality the polymer wouldhave viscosity three times the viscosity of the aforedescribed silanepolymer.

The aforedescribed components along with the additional componentsdescribed in Table 1 below were used to prepare clearcoat compositionsof Example 1 of the present invention and Comparative Examples 1 and 2.

TABLE 1 Clearcoat Compositions Comparative Comparative Example 1 Example2 Example 1 Monomeric 32 32 32 melamine¹ Blocked 58 37 Isocyanurate 1Blocked 60 Isocyanurate 2 Silane Polymer 1 28 NAD² 46 46 31 HALSTinuvin ® 2 2 2 123³ UVA Tinuvin ® 2 2 2 1130⁴ Catalyst 1⁵ 4.5 4.5 3.5Catalyst 2⁶ 0.1 ¹Cymel ® 1168 (methylated butylated melamine from CytecIndustries Inc., West Patterson, New York ² Prepared in accordance withthe U.S. Pat. No. 5,747,590 at column 8, lines 46-68 and column 9, lines1-25, all of which is incorporated herein by reference ³ Supplied byCiba Specialty Chemicals, Tarrytown, New York ⁴ Supplied by CibaSpecialty Chemicals, Tarrytown, New York ⁵ Phenyl acid phosphate salt of2-amino-2-methyl-1-propanol supplied by King Industries, Norwalk,Connecticut ⁶ Dibutyl tin dilaurate supplied by Air Product, Allentown,Pennsylvania

Layers from clearcoat compositions from Example 1 and ComparativeExamples 1 and 2 were spray applied wet-on-wet over a basecoat on aprimed phosphated steel panels and then bake cured for 30 minutes at140° C. to form coatings thereon. Applicants unexpected discovery of thedramatic improvement in the coating properties when the aforedescribedSilane Polymer 1 is added to the melamine/isocyanate components can beseen from the coating properties of Example 1 and Comparative Examples 1and 2 measured and reported in Table 2 below:

TABLE 2 Properties Comparative Comparative Properties Test MethodExample 1 Example 2 Example 1 Dry film ASTM D1400 32 microns 32 microns32 microns thickness 20° Gloss ASTM D523 84 84 94 DOI ASTM D5767 83 80.292.3 Tukon ASTM D1474 6.2 14.1 14.1 Hardness % Retention ASTM D5178 8092 98 dry mar % Retention ASTM D5178 92 81 86 wet mar Acid etchJacksonville, 8.33 6.17 5.5 Florida exposure for 3 months¹ ¹On a scaleof 1 to 10 (1 being the best and 10 being the worst).

From the data reported in Table 2 it is readily apparent that thepresence of silane polymer in the clearcoat composition substantiallyimproves the appearance of the coating with substantially comparable orbetter acid etch and mar resistances and film hardness.

What is claimed is:
 1. A clear coating composition comprisingisocyanate, silane and melamine components wherein said isocyanatecomponent comprises an aliphatic polyisocyanate having on an average 2to 6 isocyanate functionalities, wherein a VOC of said compositionvaries in the range of from 0.0 to 0.472 kilogram of an organic solventper liter of the composition wherein the composition comprises 35percent to 70 percent of said aliphatic polyisocyanate and 10 percent to40 percent of said melamine component, all the percentages being basedon total weight of composition solids.
 2. The composition of claim 1wherein said isocyanate functionalities are blocked by reacting saidfunctionalities with a monomeric alcohol.
 3. The composition of claim 2wherein said monomeric alcohol is an aliphatic alcohol.
 4. Thecomposition of claim 1 wherein said silane component comprises at leastone silane polymer having one or more reactive silane group.
 5. Thecomposition of claim 1 or 2 wherein said composition further comprisesone or more organo tin catalysts or acid catalysts.
 6. The compositionof claim 5 wherein said organo tin catalyst is selected from the groupconsisting of dibutyl tin diacetate, dibutyl tin dilaurate, stannousoctate, and a combination thereof.
 7. The composition of claim 5 whereinthe acid catalyst is selected from the group consisting ofdodecylbenzene sulfonic acid, dodecylbenzene sulfonic acid blocked withan amine, para-toluenesulfonic acid, para-toluenesulfonic acid blockedwith an amine, phenyl acid phosphate, phenyl acid phosphate blocked withan amine dinonylnaphthalene sulfonic acid, dinonylnaphthalene sulfonicacid blocked with an amine and a combination thereof.
 8. The compositionof claim 7 wherein said amine is dimethyl oxazolidine,2-amino-2-methyl-1-propanol, n,n-dimethylethanolamine or a combinationthereof.
 9. The composition of claim 5, 6 or 7 wherein said compositioncomprises in the range of from 0.001 percent to 5.0 percent of saidcatalyst, all percentages being weight percentages based on the totalweight of composition solids.
 10. The composition of claim 1 whereinsaid polyisocyanate comprises one or more trimers of hexamethylenediisocyanate, isophorone diisocyanate, meta-tetramethylxylylenediisocyanate, or a combination thereof.
 11. The composition of claim 1or 6 comprises in the range of from 35 percent to 70 percent saidpolyisocyanate wherein all percentages are in weight based on the totalweight of composition solids.
 12. The composition of claim 1, 2 or 10wherein said polyisocyanate has an average 2.5 to 6 isocyanatefunctionalities.
 13. The composition of claim 1 wherein said melaminecomponent comprises a monomeric melamine, a polymeric melamine, or acombination thereof.
 14. The composition of claim 1 or 13 comprises inthe range of from 10 percent to 40 percent of said melamine componentwherein all percentages are in weight based on the total weight ofcomposition solids.
 15. The composition of claim 1 further comprises aflow modifying resin.
 16. The composition of claim 1 comprises in therange of from 5 percent to 45 percent of said silane component, allpercentages being in weight percentages based on the total weight ofcomposition solids.
 17. The composition of claim 1 in the form of atwo-pack composition wherein a first-pack of said two-pack compositioncomprises said polyisocyanate component and a second-pack of saidtwo-pack composition comprises said melamine and silane components. 18.The clear coating composition of claim 1 wherein a clear coating on asubstrate produced from said composition has a DOI rating of at least80.
 19. The composition of claim 1 further comprises ultra violet lightstabilizers, light absorbers or a combination thereof.
 20. The clearcoating composition of claim 1 wherein said isocyanate componentcomprises 40 percent to 60 percent of said aliphatic polyisocyanate and15 percent to 35 percent of said melamine component, all the percentagesbeing based on total weight of composition solids.
 21. The clear coatingcomposition of claim 1 wherein said isocyanate component comprises 45percent to 55 percent of said aliphatic polyisocyanate and 20 percent to30 percent of said melamine component, all the percentages being basedon total weight of composition solids.
 22. A coating compositioncomprising isocyanate, silane and melamine components wherein saidisocyanate component comprises an aliphatic polyisocyanate having on anaverage 2 to 6 isocyanate functionalities wherein said silane componentcomprises a silane polymer polymerized from about 30% to 95% by weightof ethylenically unsaturated non-silane containing monomers and about 5%to 70% by weight of ethylenically unsaturated silane containing monomersbased on the weight of the silane polymer, said silane containingmonomers selected from the group consisting of: (a) a silane functionalmonomer having the structural formula (I):

 wherein R is CH₃, CH₃CH₂, CH₃O, or CH₃CH₂O; R₁ and R₂ are CH₃ orCH₃CH₂; and R₃ is H, CH₃, or CH₃CH₂; and n is 0 or a positive integerfrom 1 to 10; (b) a silane functional monomer having the structuralformula (II):

 wherein R is CH₃, CH₃CH₂, CH₃O, or CH₃CH₂O; R₁ and R₂ are CH₃ orCH₃CH₂; and n is 0 or a positive integer from 1 to 10; (c) a silanefunctional macromonomer having the structural formula (III):

 wherein R is CH₃, CH₃CH₂, CH₃O, or CH₃CH₂O; R₁ and R₂ are CH₃ orCH₃CH₂; R₃ is an alkylene group having 1 to 8 carbon atoms; R₄ is H orCH₃; and n is a positive integer from 1 to 8; (d) acyloxysilane; (e)vinylacetoxy silane; and a combination thereof.
 23. The coatingcomposition of claim 22 wherein said silane functional monomer offormula (I) is gamma-acryloxypropyltrimethoxy silane,gamma-methacryloxypropyltrimethoxy silane,gamma-methacryloxypropyltris(2-methoxyethoxy)silane, or a combinationthereof.
 24. The coating composition of claim 22 wherein said silanefunctional monomer of formula (II) is vinyltrimethoxy silane,vinyltriethoxy silane, vinyltris(2-methoxyethoxy)silane, or acombination thereof.
 25. The coating composition of claim 22 whereinsaid silane polymer is polymerized from about 15 to 25% by weightstyrene, about 30 to 60% by weight methacryloxypropyltrimethoxy silane,and about 25 to 50% by weight trimethylcyclohexyl methacrylate.
 26. Theclear coating composition of claim 22 wherein said silane polymer ispolymerized from about 30% by weight styrene, about 50% by weightmethacryloxypropyl trimethoxy silane, and about 20% by weight ofnonfunctional acrylates, methacrylates or any mixtures thereof.
 27. Acoating composition comprising isocyanate, silane and melaminecomponents wherein said isocyanate component comprises an aliphaticpolyisocyanate having on an average 2 to 6 isocyanate functionalities,wherein said isocyanate component comprises 35 percent to 70 percent ofsaid aliphatic polyisocyanate and 10 percent to 40 percent of saidmelamine component, all the percentages being based on total weight ofcomposition solids.
 28. A clear coating composition comprisingisocyanate, silane and melamine components wherein said isocyanatecomponent comprises an aliphatic polyisocyanate having on an average 2to 6 isocyanate functionalities, said composition being in the form of atwo-pack composition wherein a first-pack of said two-pack compositioncomprises said isocyanate component and a second-pack of said two-packcomposition comprises said melamine and silane components.
 29. A low VOCclear coating composition comprising isocyanate, silane and melaminecomponents wherein said isocyanate component comprises an aliphaticpolyisocyanate having on an average 2 to 6 isocyanate functionalities,said composition being in the form of a two-pack composition wherein afirst-pack of said two-pack composition comprises said isocyanatecomponent and a second-pack of said two-pack composition comprises saidmelamine and silane components.
 30. A method of producing a clearcoating on a substrate comprising: applying a layer of a clear coatingcomposition comprising isocyanate, silane and melamine componentswherein said isocyanate component comprises an aliphatic polyisocyanatehaving on an average 2 to 6 isocyanate functionalities, wherein a VOC ofsaid composition varies in the range of from 0.0 to 0.472 kilogram of anorganic solvent per liter of the composition; and curing said layer intosaid clear coating.
 31. The method of claim 30 wherein said coating hasa DOI rating of at least
 80. 32. The method of claim 30 wherein saidcoating has a 20° gloss of at least
 80. 33. The method of claim 30wherein said isocyanate functionalities of the polyisocyanate areblocked by reacting said polyisocyanate with a monomeric alcohol. 34.The method of claim 33 wherein said monomeric alcohol is cyclohexanol,2-ethyl hexanol or a mixture thereof.
 35. The method of claim 33 or 34wherein said curing of said layer takes place at an elevated bakingtemperature in the range 80° C. to 160° C.
 36. The method of claim 30wherein said composition comprises in the range of from 5 percent to 45percent of said silane component, all percentages being in weightpercentages based on the total weight of composition solids.